An MRAM (Magnetic Random Access Memory) using a ferromagnetic material is expected as a nonvolatile memory endowed with nonvolatileness, high operation speed, large capacity, and low power consumption. The MRAM includes MTJ (Magnetic Tunnel Junction) elements using the TMR (Tunneling MagnetoResistive) effect as memory elements, and stores information based on the magnetization states of the MTJ elements. A perpendicular magnetization MTJ element has been proposed as an MTJ element, which stores information by generating magnetization perpendicular to the film surface.
The MTJ element includes a storage layer having a variable magnetization direction, and a reference layer having an invariable magnetization direction. The storage layer is stacked on a tunnel barrier layer on the reference layer. In the perpendicular magnetization MTJ element, the reference layer and the storage layer have different sizes. More specifically, the reference layer has, on the plane, a diameter larger than that of the storage layer located above. That is, the MTJ element has a step shape in the section. The reference layer includes an interface layer having a high polarization rate near the interface to the tunnel barrier layer to obtain a high magnetoresistive ratio necessary for reading information.
In general, perpendicular magnetic anisotropy is generated in the interface between the tunnel barrier layer and the interface layer. However, in the process of forming the above-described step structure, the tunnel barrier layer having an exposed surface is nonuniformly etched, and the crystal structure is distorted. Hence, the perpendicular magnetic anisotropy of the interface layer disappears, and the perpendicular magnetic anisotropy of the reference layer becomes unstable.